1. Field of the Invention
This present invention generally relates to an antenna, and more particularly to a dual-band dipole antenna for wireless local area network (WLAN) system.
2. Description of the Related Art
The prosperous development of wireless communication industry brings various products and techniques for multi-band communication such that many new products have the performance for wireless communication so as to meet the consumers"" demand. For example, the inconvenience of wiring and setting owing to the frequent data transmission of a laptop computer is simplified by means of wireless communication devices. Accordingly, the design of an antenna is essential to achieve the purpose for wireless communication. Moreover, if a laptop computer with wireless communication functions desires to be widely accepted and appreciated in the market, the appearance, size, and performance thereof are very critical. Therefore it is relatively essential for a laptop computer to have a well-designed antenna.
Conventional antennas generally adapted to wireless communication products such as laptop computers are substantially grouped into two types, wherein one is the planar inverted F antenna (PIFA) and the other is the monopole antenna. Such two types can generate the operating modes of xc2xc wavelength resonance. For example, U.S. Pat. No. 5,926,139 issued to Korisch on Jul. 20, 1999 discloses a planar antenna for use in a radio transceiver device comprising a planar dielectric substrate having first and second surfaces; a first layer on the first surface; a unitary second layer on the second surface having two radiating portion functioning as planar inverted F antennas (PIFA), and a connecting portion joining the radiating portions; a grounding pin; and a feed pin. However, the ground pin must extend through the substrate and interconnect the first layer and the connecting portion of the second layer structurally and thus it is found that the fabrication of the antenna is quite difficult and complicated. In addition, such a planar inverted F antenna typically has a narrow bandwidth such that the usage thereof is disadvantageously restricted. While the monopole antenna has a relatively great bandwidth, a considerably wide ground plane is required for achieving the desired radiation efficiency. Because the space provided in a laptop computer to dispose an antenna is relatively slender, the monopole antenna is also limited in usage.
Furthermore, conventional antennas are merely able to operate in a single band at the most, such as U.S. Pat. No. 6,008,774 issued to Wu on Dec. 28, 1999 entitled xe2x80x9cPrinted antenna structure for wireless data communicationxe2x80x9d, which discloses a printed antenna including a printed circuit board, a hook-shaped radiating metallic line printed on the top surface of the printed circuit board, a feeding point connected to the hook-shaped radiating metallic line, and a ground plane printed on the bottom surface of the printed circuit board. However, this antenna only operates in the 2.4 GHz band for WLAN operations. Therefore, it can be expected that, with the growing market, the performance and market competitiveness of the antenna only operated in a single frequency band will be insufficient. Accordingly, to develop an antenna adapted for dual frequency bands is the mainstream trend of related electronic products.
Accordingly, it is necessary to provide a dual-band dipole antenna, which is able to operate in dual frequency bands (such as 2.4 and 5.2 GHz bands) and has a compact shape particularly adapted to the communication products such as laptop computers so as to achieve the purpose of hiding the antenna and keeping the products ornamental.
It is a primary object of the present invention to provide a dual-band dipole antenna which is capable of operating in dual frequency bands for WLAN operations.
It is another object of the present invention to provide a dual-band dipole antenna which has a compact shape particularly adapted to the communication products such as laptop computers.
To achieve the aforementioned objects, the present invention provides a dual-band dipole antenna, which is adapted to be disposed on a dielectric substrate and comprises two substantially rectangular radiating metallic sheets and a coaxial transmission line. The substantially rectangular radiating metallic sheets are symmetrically disposed on two sides of a dielectric substrate with respect to the central line thereof, wherein each of the radiating metallic sheets further has a feeding point and a slit. One feeding point is disposed opposite to the other feeding point, and the slit extends from one edge of the substantially rectangular radiating metallic sheet in the direction of the feeding point to the interior thereof so that a longer path and a shorter one are formed on the substantially rectangular radiating metallic sheet. The coaxial transmission line has a core conductor and an external ground conductor which are respectively connected to the feeding points.
According to another aspect of the present invention, the longer path serves to generate a first (lower frequency) operating mode of the dual-band dipole antenna, and the shorter one serves to generate a second (higher frequency) operating mode thereof.
According to a further aspect of the present invention, the length of the longer path is selected to be approximately xc2xc wavelength of the central frequency of the first operating mode and that of the smaller sub-metallic is selected to be approximately xc2xc wavelength of the central frequency of the second operating mode.
According to a still further aspect of the present invention, the central frequency of the first operating mode is around 2.4 GHz.
According to a still further aspect of the present invention, the central frequency of the second operating mode is around 5.2 GHz.